Approved Parts: TSO and ETSO Mutual Acceptance

By Jason Dickstein

Just in case you are pressed for time, I will give you the quick summary. The U. S. and Europe are investigating how to accomplish mutual acceptance of TSOAs and ETSOAs. This is a huge advance for the aviation community, that is expected to save both industry and government resources.

Now let’s delve into some details…

What is a TSO?
In the Europe and the United States, many aircraft components are manufactured to a common standard, known as a Technical Standard Order or TSO (an ETSO in the EU). TSOs are typically used for components that may be common to a number of different types. This can include components like avionics, seats, seat belts, and emergency equipment.

The theory of a TSO is that a part that meets the minimum standards of a TSO ought to be able to function appropriately in aircraft that needs a component of that sort. A company that wants to produce parts that meet the minimum standards of a TSO must apply for government approval in order to do so. In the United States this is called a TSOA or Technical Standard Order Authorization. Generally, the TSOA applicant must self-certify design compliance, although the FAA is permitted to check compliance to the extent that the FAA believes necessary. In addition, the TSOA applicant must have a production quality assurance system that meets FAA regulatory requirements and that will be subject to FAA inspection through FAA Manufacturing Inspection District Offices, known as MIDOs. An FAA-approved production quality assurance system helps to ensure that each component that is produced under the TSOA design, will meet the specifications of the TSOA design.

Because a TSOA article is theoretically installable in any aircraft, it carries no inherent installation eligibility. So if an installer gets a TSOA article with no other data, the component may not be able to install the article in any aircraft. The path toward installation of a TSOA article typically involves additional scrutiny and data that shows that the installation in a particular aircraft or type meets FAA regulatory/safety requirements. Where the TSOA article reflects a major change to type design, it may require a supplemental type certificate (STC) in order to approve the installation/modification data.

Measuring Quality
One of the ways that companies measure the quality of an aircraft part is through the strength of the system that stands behind it. The system is always going to be made up of multiple parts. They will include the company’s own quality assurance system as well as the oversight that helps to ensure the integrity of that quality assurance system. Oversight can be internal, through internal auditing that helps to ensure that the company operates the way that management expects. Oversight can be external, through other-party auditors who are brought in to ensure that the company meets the standards that it expects to meet. And external oversight can include regulatory oversight by the local civil aviation authority.

In the United States, regulatory oversight by the local civil aviation authority (the Federal Aviation Administration, or FAA) has been considered to be important since the beginnings of commercial aviation. FAA oversight helps to make the public comfortable with the idea that the aerospace industry remains compliant with safety standards.
As a consequence, the FAA is loath to surrender any of its approval authority. Not because the FAA is power-mad like a Bond villain … but rather because the FAA does not want to betray that public trust.

Acceptance of Foreign Components
The FAA approves components manufactured under TSOA; components produced under foreign standards are not inherently acceptable to the United States. The United States may accept foreign-produced articles when the FAA itself has approved the design (using a Letter of Design Approval or LODA) AND the United States has signed a bilateral agreement with the foreign nation that accepts LODA designs that are produced under the foreign airworthiness authority’s manufacturing oversight.

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